Stimulating intra- and intermolecular charge transfer and nonlinear optical response for biphenalenyl biradicaloid dimer under an external electric field

An interesting biphenalenyl biradicaloid (IDPL) dimer consisting of both-middle superimposed phenalenyls and both-end nonsuperimposed phenalenyls has been synthesized, and has attracted intensive research interest due to its intra-and intermolecular interactions and semiconductive characteristics. It is significant that under regulation of the external electric field the directional charge transfer (CT) can produce attractive properties. In the present work, the structure and electronic properties of the IDPL dimer under an external electric field (along the horizontal F-x or the vertical F-z directions) are explored, and the following properties determined: (i) as the horizontal F-x increases, the intramolecular CT becomes larger, which induces the intermolecular CT of the IDPL dimer. (ii) In contrast, as the vertical F-z increases, the large intermolecular CT gives rise to the intramolecular CT of the IDPL dimer. (iii) More importantly, the external electric field effectively regulates and controls the first hyperpolarizability (beta(tot)) of the IDPL dimer. Compared with the vertical F-z, the horizontal F-x induces a larger first hyperpolarizability (beta(tot) = 5.48 x 10(5) a.u.). Furthermore, the application of a uniform external electric field (F-x,F-y,F-z) to the IDPL dimer was investigated to define the external electric field direction of the material application. The beta(tot) values were increased with increasing of the uniform F-x,F-y,F-z. Our study provides an effective strategy for developing high-performance NLO materials by tuning the external electric field, and could be of significance for application in switch devices.